The stereochemistry of ligand bindings will be determined by epr on CoMb1702, 57Mb15NO and CoMb13CO. The unpaired electron density distribution in CoHb will be measured by isotropic contact shifts. These experimental investigations will be supplemented by theoretical studies. The cofactor bindings and CO2 equilibria with Hb and erythrocytes will be studied. CoHb will be used to test rigorously the current models for allosteric enzymes. This includes work also on hybrid Fe and Co hemoglobins. The structure of CoHb will be determined by x-ray diffraction. Sensitive methods to reveal differences in reactivities and properties of Hbs as compared to normal Hb will be developed. Heme plane orientation will be determined on single crystals of spin labeled Hbs and CoHbs. The rate and mechanism of pseudohomogeneous electron transfer between CoHb and Fe Hb will be studied. The undersigned agrees to accept responsibility for the scientific and technical conduct of the project and for provision required progress reports if a grant is awarded as the result of this application.